Capacitive Force Sensor

ABSTRACT

In one embodiment, a method includes detecting movement of a spring structure of a force sensor coupled to a center shaft of an active stylus; measuring a change of capacitance between electrodes of the force sensor; and determining an amount of force applied to the center shaft based on the change of capacitance.

RELATED APPLICATION

This application claims the benefit, under 35 U.S.C. §119(e), of U.S.Provisional Patent Application No. 61/553,114, filed 28 Oct. 2011, whichis incorporated herein by reference.

TECHNICAL FIELD

This disclosure generally relates to touch sensors.

BACKGROUND

A touch-position sensor, or a touch sensor, may detect the presence andlocation of an object or the proximity of an object (such as a user'sfinger or a stylus) within a touch-sensitive area of the touch sensoroverlaid, for example, on a display screen. In a touch sensitive displayapplication, the touch position sensor may enable a user to interactdirectly with what is displayed on the screen, rather than indirectlywith a mouse or touch pad. A touch sensor may be attached to or providedas a part of a desktop computer, laptop computer, tablet computer,personal digital assistant (PDA), smartphone, satellite navigationdevice, portable media player, portable game console, kiosk computer,point-of-sale device, or other suitable device. A control panel on ahousehold or other appliance may include a touch sensor.

There are a number of different types of touch position sensors, such as(for example) resistive touch screens, surface acoustic wave touchscreens, and capacitive touch screens. Herein, reference to a touchsensor may encompass a touch screen, and vice versa, where appropriate.When an object touches or comes within proximity of the surface of thecapacitive touch screen, a change in capacitance may occur within thetouch screen at the location of the touch or proximity. A controller mayprocess the change in capacitance to determine its position on the touchscreen.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example touch sensor with an example controller.

FIG. 2 illustrates an example exterior of an example active stylus.

FIG. 3 illustrates an example internal components of example activestylus.

FIG. 4 illustrates an example active stylus with an example device.

FIG. 5 illustrates an example force sensor of the example stylus of FIG.3.

FIG. 6 illustrates an example method for measuring force applied to anactive stylus.

DESCRIPTION OF EXAMPLE EMBODIMENTS

FIG. 1 illustrates an example touch sensor 10 with an example controller12. Touch sensor 10 and touch-sensor controller 12 may detect thepresence and location of a touch or the proximity of an object within atouch-sensitive area of touch sensor 10. Herein, reference to a touchsensor may encompass both the touch sensor and its touch-sensorcontroller, where appropriate. Similarly, reference to a touch-sensorcontroller may encompass both the touch-sensor controller and its touchsensor, where appropriate. Touch sensor 10 may include one or moretouch-sensitive areas, where appropriate. Touch sensor 10 may include anarray of drive and sense electrodes (or an array of electrodes of asingle type) disposed on one or more substrates, which may be made of adielectric material. Herein, reference to a touch sensor may encompassboth the electrodes of the touch sensor and the substrate(s) that theyare disposed on, where appropriate. Alternatively, where appropriate,reference to a touch sensor may encompass the electrodes of the touchsensor, but not the substrate(s) that they are disposed on.

An electrode (whether a ground electrode, a guard electrode, a driveelectrode, or a sense electrode) may be an area of conductive materialforming a shape, such as for example a disc, square, rectangle, othersuitable shape, or suitable combination of these. One or more cuts inone or more layers of conductive material may (at least in part) createthe shape of an electrode, and the area of the shape may (at least inpart) be bounded by those cuts. In particular embodiments, theconductive material of an electrode may occupy approximately 100% of thearea of its shape. As an example and not by way of limitation, anelectrode may be made of indium tin oxide (ITO) and the ITO of theelectrode may occupy approximately 100% of the area of its shape, whereappropriate. In particular embodiments, the conductive material of anelectrode may occupy substantially less than 100% of the area of itsshape. As an example and not by way of limitation, an electrode may bemade of fine lines of metal or other conductive material (such as forexample copper, silver, or a copper- or silver-based material) and thefine lines of conductive material may occupy substantially less than100% of the area of its shape in a hatched, mesh, or other suitablepattern. Although this disclosure describes or illustrates particularelectrodes made of particular conductive material forming particularshapes with particular fills having particular patterns, this disclosurecontemplates any suitable electrodes made of any suitable conductivematerial forming any suitable shapes with any suitable fills having anysuitable patterns. Where appropriate, the shapes of the electrodes (orother elements) of a touch sensor may constitute in whole or in part oneor more macro-features of the touch sensor. One or more characteristicsof the implementation of those shapes (such as, for example, theconductive materials, fills, or patterns within the shapes) mayconstitute in whole or in part one or more micro-features of the touchsensor. One or more macro-features of a touch sensor may determine oneor more characteristics of its functionality, and one or moremicro-features of the touch sensor may determine one or more opticalfeatures of the touch sensor, such as transmittance, refraction, orreflection.

A mechanical stack may contain the substrate (or multiple substrates)and the conductive material forming the drive or sense electrodes oftouch sensor 10. As an example and not by way of limitation, themechanical stack may include a first layer of optically clear adhesive(OCA) beneath a cover panel. The cover panel may be clear and made of aresilient material suitable for repeated touching, such as for exampleglass, polycarbonate, or poly(methyl methacrylate) (PMMA). Thisdisclosure contemplates any suitable cover panel made of any suitablematerial. The first layer of OCA may be disposed between the cover paneland the substrate with the conductive material forming the drive orsense electrodes. The mechanical stack may also include a second layerof OCA and a dielectric layer (which may be made of PET or anothersuitable material, similar to the substrate with the conductive materialforming the drive or sense electrodes). As an alternative, whereappropriate, a thin coating of a dielectric material may be appliedinstead of the second layer of OCA and the dielectric layer. The secondlayer of OCA may be disposed between the substrate with the conductivematerial making up the drive or sense electrodes and the dielectriclayer, and the dielectric layer may be disposed between the second layerof OCA and an air gap to a display of a device including touch sensor 10and touch-sensor controller 12. As an example only and not by way oflimitation, the cover panel may have a thickness of approximately 1millimeter (mm); the first layer of OCA may have a thickness ofapproximately 0.05 mm; the substrate with the conductive materialforming the drive or sense electrodes may have a thickness ofapproximately 0.05 mm; the second layer of OCA may have a thickness ofapproximately 0.05 mm; and the dielectric layer may have a thickness ofapproximately 0.05 mm. Although this disclosure describes a particularmechanical stack with a particular number of particular layers made ofparticular materials and having particular thicknesses, this disclosurecontemplates any suitable mechanical stack with any suitable number ofany suitable layers made of any suitable materials and having anysuitable thicknesses. As an example and not by way of limitation, inparticular embodiments, a layer of adhesive or dielectric may replacethe dielectric layer, second layer of OCA, and air gap described above,with there being no air gap to the display.

One or more portions of the substrate of touch sensor 10 may be made ofpolyethylene terephthalate (PET) or another suitable material. Thisdisclosure contemplates any suitable substrate with any suitableportions made of any suitable material. In particular embodiments, thedrive or sense electrodes in touch sensor 10 may be made of ITO in wholeor in part. In particular embodiments, the drive or sense electrodes intouch sensor 10 may be made of fine lines of metal or other conductivematerial. As an example and not by way of limitation, one or moreportions of the conductive material may be copper or copper-based andhave a thickness of approximately 5 microns (μm) or less and a width ofapproximately 10 μm or less. As another example, one or more portions ofthe conductive material may be silver or silver-based and similarly havea thickness of approximately 5 μm or less and a width of approximately10 μm or less. This disclosure contemplates any suitable electrodes madeof any suitable material.

Touch sensor 10 may implement a capacitive form of touch sensing. In amutual-capacitance implementation, touch sensor 10 may include an arrayof drive and sense electrodes forming an array of capacitive nodes. Adrive electrode and a sense electrode may form a capacitive node. Thedrive and sense electrodes forming the capacitive node may come neareach other, but not make electrical contact with each other. Instead,the drive and sense electrodes may be capacitively coupled to each otheracross a space between them. A pulsed or alternating voltage applied tothe drive electrode (by touch-sensor controller 12) may induce a chargeon the sense electrode, and the amount of charge induced may besusceptible to external influence (such as a touch or the proximity ofan object). When an object touches or comes within proximity of thecapacitive node, a change in capacitance may occur at the capacitivenode and touch-sensor controller 12 may measure the change incapacitance. By measuring changes in capacitance throughout the array,touch-sensor controller 12 may determine the position of the touch orproximity within the touch-sensitive area(s) of touch sensor 10.

In a self-capacitance implementation, touch sensor 10 may include anarray of electrodes of a single type that may each form a capacitivenode. When an object touches or comes within proximity of the capacitivenode, a change in self-capacitance may occur at the capacitive node andtouch-sensor controller 12 may measure the change in capacitance, forexample, as a change in the amount of charge needed to raise the voltageat the capacitive node by a pre-determined amount. As with amutual-capacitance implementation, by measuring changes in capacitancethroughout the array, touch-sensor controller 12 may determine theposition of the touch or proximity within the touch-sensitive area(s) oftouch sensor 10. This disclosure contemplates any suitable form ofcapacitive touch sensing, where appropriate.

In particular embodiments, one or more drive electrodes may togetherform a drive line running horizontally or vertically or in any suitableorientation. Similarly, one or more sense electrodes may together form asense line running horizontally or vertically or in any suitableorientation. In particular embodiments, drive lines may runsubstantially perpendicular to sense lines. Herein, reference to a driveline may encompass one or more drive electrodes making up the driveline, and vice versa, where appropriate. Similarly, reference to a senseline may encompass one or more sense electrodes making up the senseline, and vice versa, where appropriate.

Touch sensor 10 may have drive and sense electrodes disposed in apattern on one side of a single substrate. In such a configuration, apair of drive and sense electrodes capacitively coupled to each otheracross a space between them may form a capacitive node. For aself-capacitance implementation, electrodes of only a single type may bedisposed in a pattern on a single substrate. In addition or as analternative to having drive and sense electrodes disposed in a patternon one side of a single substrate, touch sensor 10 may have driveelectrodes disposed in a pattern on one side of a substrate and senseelectrodes disposed in a pattern on another side of the substrate.Moreover, touch sensor 10 may have drive electrodes disposed in apattern on one side of one substrate and sense electrodes disposed in apattern on one side of another substrate. In such configurations, anintersection of a drive electrode and a sense electrode may form acapacitive node. Such an intersection may be a location where the driveelectrode and the sense electrode “cross” or come nearest each other intheir respective planes. The drive and sense electrodes do not makeelectrical contact with each other—instead they are capacitively coupledto each other across a dielectric at the intersection. Although thisdisclosure describes particular configurations of particular electrodesforming particular nodes, this disclosure contemplates any suitableconfiguration of any suitable electrodes forming any suitable nodes.Moreover, this disclosure contemplates any suitable electrodes disposedon any suitable number of any suitable substrates in any suitablepatterns.

As described above, a change in capacitance at a capacitive node oftouch sensor 10 may indicate a touch or proximity input at the positionof the capacitive node. Touch-sensor controller 12 may detect andprocess the change in capacitance to determine the presence and locationof the touch or proximity input. Touch-sensor controller 12 may thencommunicate information about the touch or proximity input to one ormore other components (such one or more central processing units (CPUs)or digital signal processors (DSPs)) of a device that includes touchsensor 10 and touch-sensor controller 12, which may respond to the touchor proximity input by initiating a function of the device (or anapplication running on the device) associated with it. Although thisdisclosure describes a particular touch-sensor controller havingparticular functionality with respect to a particular device and aparticular touch sensor, this disclosure contemplates any suitabletouch-sensor controller having any suitable functionality with respectto any suitable device and any suitable touch sensor.

Touch-sensor controller 12 may be one or more integrated circuits (ICs),such as for example general-purpose microprocessors, microcontrollers,programmable logic devices or arrays, application-specific ICs (ASICs).In particular embodiments, touch-sensor controller 12 comprises analogcircuitry, digital logic, and digital non-volatile memory. In particularembodiments, touch-sensor controller 12 is disposed on a flexibleprinted circuit (FPC) bonded to the substrate of touch sensor 10, asdescribed below. The FPC may be active or passive. In particularembodiments, multiple touch-sensor controllers 12 are disposed on theFPC. Touch-sensor controller 12 may include a processor unit, a driveunit, a sense unit, and a storage unit. The drive unit may supply drivesignals to the drive electrodes of touch sensor 10. The sense unit maysense charge at the capacitive nodes of touch sensor 10 and providemeasurement signals to the processor unit representing capacitances atthe capacitive nodes. The processor unit may control the supply of drivesignals to the drive electrodes by the drive unit and processmeasurement signals from the sense unit to detect and process thepresence and location of a touch or proximity input within thetouch-sensitive area(s) of touch sensor 10. The processor unit may alsotrack changes in the position of a touch or proximity input within thetouch-sensitive area(s) of touch sensor 10. The storage unit may storeprogramming for execution by the processor unit, including programmingfor controlling the drive unit to supply drive signals to the driveelectrodes, programming for processing measurement signals from thesense unit, and other suitable programming, where appropriate. Althoughthis disclosure describes a particular touch-sensor controller having aparticular implementation with particular components, this disclosurecontemplates any suitable touch-sensor controller having any suitableimplementation with any suitable components.

Tracks 14 of conductive material disposed on the substrate of touchsensor 10 may couple the drive or sense electrodes of touch sensor 10 toconnection pads 16, also disposed on the substrate of touch sensor 10.As described below, connection pads 16 facilitate coupling of tracks 14to touch-sensor controller 12. Tracks 14 may extend into or around (e.g.at the edges of) the touch-sensitive area(s) of touch sensor 10.Particular tracks 14 may provide drive connections for couplingtouch-sensor controller 12 to drive electrodes of touch sensor 10,through which the drive unit of touch-sensor controller 12 may supplydrive signals to the drive electrodes. Other tracks 14 may provide senseconnections for coupling touch-sensor controller 12 to sense electrodesof touch sensor 10, through which the sense unit of touch-sensorcontroller 12 may sense charge at the capacitive nodes of touch sensor10. Tracks 14 may be made of fine lines of metal or other conductivematerial. As an example and not by way of limitation, the conductivematerial of tracks 14 may be copper or copper-based and have a width ofapproximately 100 μm or less. As another example, the conductivematerial of tracks 14 may be silver or silver-based and have a width ofapproximately 100 μm or less. In particular embodiments, tracks 14 maybe made of ITO in whole or in part in addition or as an alternative tofine lines of metal or other conductive material. Although thisdisclosure describes particular tracks made of particular materials withparticular widths, this disclosure contemplates any suitable tracks madeof any suitable materials with any suitable widths. In addition totracks 14, touch sensor 10 may include one or more ground linesterminating at a ground connector (which may be a connection pad 16) atan edge of the substrate of touch sensor 10 (similar to tracks 14).

Connection pads 16 may be located along one or more edges of thesubstrate, outside the touch-sensitive area(s) of touch sensor 10. Asdescribed above, touch-sensor controller 12 may be on an FPC. Connectionpads 16 may be made of the same material as tracks 14 and may be bondedto the FPC using an anisotropic conductive film (ACF). Connection 18 mayinclude conductive lines on the FPC coupling touch-sensor controller 12to connection pads 16, in turn coupling touch-sensor controller 12 totracks 14 and to the drive or sense electrodes of touch sensor 10. Inanother embodiment, connection pads 16 may be connected to anelectro-mechanical connector (such as a zero insertion forcewire-to-board connector); in this embodiment, connection 18 may not needto include an FPC. This disclosure contemplates any suitable connection18 between touch-sensor controller 12 and touch sensor 10.

FIG. 2 illustrates an example exterior of an example active stylus 20.In particular embodiments, active stylus 20 is powered (e.g., by aninternal or external power source) and is capable of providing touch orproximity inputs to a touch sensor (e.g., touch sensor 10 illustrated inFIG. 1). Active stylus 20 may include one or more components, such asbuttons 30 or sliders 32 and 34 integrated with an outer body 22. Theseexternal components may provide for interaction between active stylus 20and a user or between a device and a user. As an example and not by wayof limitation, interactions may include communication between activestylus 20 and a device, enabling or altering functionality of activestylus 20 or a device, or providing feedback to or accepting input fromone or more users. The device may by any suitable device, such as, forexample and without limitation, a desktop computer, laptop computer,tablet computer, personal digital assistant (PDA), smartphone, satellitenavigation device, portable media player, portable game console, kioskcomputer, point-of-sale device, or other suitable device. Although thisdisclosure provides specific examples of particular componentsconfigured to provide particular interactions, this disclosurecontemplates any suitable component configured to provide any suitableinteraction. Active stylus 20 may have any suitable dimensions withouter body 22 made of any suitable material or combination of materials,such as, for example and without limitation, plastic or metal. Inparticular embodiments, exterior components (e.g. 30 or 32) of activestylus 20 may interact with internal components or programming of activestylus 20 or may initiate one or more interactions with one or moredevices or other active styluses 20.

As described above, actuating one or more particular components mayinitiate an interaction between active stylus 20 and a user or betweenthe device and the user. Components of active stylus 20 may include oneor more buttons 30 or one or more sliders 32 and 34. As an example andnot by way of limitation, buttons 30 or sliders 32 and 34 may bemechanical or capacitive and may function as a roller, trackball, orwheel. As another example, one or more sliders 32 or 34 may function asa vertical slider 34 aligned along a longitudinal axis of active stylus20, while one or more wheel sliders 32 may be aligned around thecircumference of active stylus 20. In particular embodiments, capacitivesliders 32 and 34 or buttons 30 may be implemented using one or moretouch-sensitive areas. Touch-sensitive areas may have any suitableshape, dimensions, location, or be made from any suitable material. Asan example and not by way of limitation, sliders 32 and 34 or buttons 30may be implemented using areas of flexible mesh formed using lines ofconductive material. As another example, sliders 32 and 34 or buttons 30may be implemented using a FPC.

Active stylus 20 may have one or more components configured to providefeedback to or accepting feedback from a user, such as, for example andwithout limitation, tactile, visual, or audio feedback. Active stylus 20may include one or more ridges or grooves 24 on its outer body 22.Ridges or grooves 24 may have any suitable dimensions, have any suitablespacing between ridges or grooves, or be located at any suitable area onouter body 22 of active stylus 20. As an example and not by way oflimitation, ridges 24 may enhance a user's grip on outer body 22 ofactive stylus 20 or provide tactile feedback to or accept tactile inputfrom a user. Active stylus 20 may include one or more audio components38 capable of transmitting and receiving audio signals. As an exampleand not by way of limitation, audio component 38 may contain amicrophone capable of recording or transmitting one or more users'voices. As another example, audio component 38 may provide an auditoryindication of a power status of active stylus 20. Active stylus 20 mayinclude one or more visual feedback components 36, such as alight-emitting diode (LED) indicator or electrophoretic ink (E-Ink). Asan example and not by way of limitation, visual feedback component 36may indicate a power status of active stylus 20 to the user.

One or more modified surface areas 40 may form one or more components onouter body 22 of active stylus 20. Properties of modified surface areas40 may be different than properties of the remaining surface of outerbody 22. As an example and not by way of limitation, modified surfacearea 40 may be modified to have a different texture, temperature, orelectromagnetic characteristic relative to the surface properties of theremainder of outer body 22. Modified surface area 40 may be capable ofdynamically altering its properties, for example by using hapticinterfaces or rendering techniques. A user may interact with modifiedsurface area 40 to provide any suitable functionally. For example andnot by way of limitation, dragging a finger across modified surface area40 may initiate an interaction, such as data transfer, between activestylus 20 and a device.

One or more components of active stylus 20 may be configured tocommunicate data between active stylus 20 and the device. For example,active stylus 20 may include one or more tips 26 or nibs. Tip 26 mayinclude one or more electrodes configured to communicate data betweenactive stylus 20 and one or more devices or other active styluses. Tip26 may provide or communicate pressure information (e.g., the amount ofpressure being exerted by active stylus 20 through tip 26) betweenactive stylus 20 and one or more devices or other active styluses. Tip26 may be made of any suitable material, such as a conductive material,and have any suitable dimensions, such as, for example, a diameter of 1mm or less at its terminal end. Active stylus 20 may include one or moreports 28 located at any suitable location on outer body 22 of activestylus 20. Port 28 may be configured to transfer signals or informationbetween active stylus 20 and one or more devices or power sources via,for example, wired coupling. Port 28 may transfer signals or informationby any suitable technology, such as, for example, by universal serialbus (USB) or Ethernet connections. Although this disclosure describesand illustrates a particular configuration of particular components withparticular locations, dimensions, composition and functionality, thisdisclosure contemplates any suitable configuration of suitablecomponents with any suitable locations, dimensions, composition, andfunctionality with respect to active stylus 20.

FIG. 3 illustrates example internal components of example active stylus20. Active stylus 20 includes one or more internal components, such as acontroller 50, sensors 42, memory 44, or power source 48. In particularembodiments, one or more internal components may be configured toprovide for interaction between active stylus 20 and a user or between adevice and a user. In other particular embodiments, one or more internalcomponents, in conjunction with one or more external componentsdescribed above, may be configured to provide interaction between activestylus 20 and a user or between a device and a user. As an example andnot by way of limitation, interactions may include communication betweenactive stylus 20 and a device, enabling or altering functionality ofactive stylus 20 or a device, or providing feedback to or acceptinginput from one or more users. As another example, active stylus 20 maycommunicate via any applicable short distance, low energy datatransmission or modulation link, such as, for example and withoutlimitation, via a radio frequency (RF) communication link. In this case,active stylus 20 includes a RF device for transmitting data over the RFlink.

Controller 50 may be a microcontroller or any other type of processorsuitable for controlling the operation of active stylus 20. Controller50 may be one or more ICs—such as, for example, general-purposemicroprocessors, microcontrollers, PLDs, PLAs, or ASICs. Controller 50may include a processor unit, a drive unit, a sense unit, and a storageunit. The drive unit may supply signals to electrodes of tip 26 throughcenter shaft 41. The drive unit may also supply signals to control ordrive sensors 42 or one or more external components of active stylus 20.The sense unit may sense signals received by electrodes of tip 26through center shaft 41 and provide measurement signals to the processorunit representing input from a device. The sense unit may also sensesignals generated by sensors 42 or one or more external components andprovide measurement signals to the processor unit representing inputfrom a user. The processor unit may control the supply of signals to theelectrodes of tip 26 and process measurement signals from the sense unitto detect and process input from the device. The processor unit may alsoprocess measurement signals from sensors 42 or one or more externalcomponents. The storage unit may store programming for execution by theprocessor unit, including programming for controlling the drive unit tosupply signals to the electrodes of tip 26, programming for processingmeasurement signals from the sense unit corresponding to input from thedevice, programming for processing measurement signals from sensors 42or external components to initiate a pre-determined function or gestureto be performed by active stylus 20 or the device, and other suitableprogramming, where appropriate. As an example and not by way oflimitation, programming executed by controller 50 may electronicallyfilter signals received from the sense unit. Although this disclosuredescribes a particular controller 50 having a particular implementationwith particular components, this disclosure contemplates any suitablecontroller having any suitable implementation with any suitablecomponents.

In particular embodiments, active stylus 20 may include one or moresensors 42, such as touch sensors, gyroscopes, accelerometers, contactsensors, or any other type of sensor that detect or measure data aboutthe environment in which active stylus 20 operates. Sensors 42 maydetect and measure one or more characteristic of active stylus 20, suchas acceleration or movement, orientation, contact, pressure on outerbody 22, force on tip 26, vibration, or any other suitablecharacteristic of active stylus 20. As an example and not by way oflimitation, sensors 42 may be implemented mechanically, electronically,or capacitively. As described above, data detected or measured bysensors 42 communicated to controller 50 may initiate a pre-determinedfunction or gesture to be performed by active stylus 20 or the device.In particular embodiments, data detected or received by sensors 42 maybe stored in memory 44. Memory 44 may be any form of memory suitable forstoring data in active stylus 20. In other particular embodiments,controller 50 may access data stored in memory 44. As an example and notby way of limitation, memory 44 may store programming for execution bythe processor unit of controller 50. As another example, data measuredby sensors 42 may be processed by controller 50 and stored in memory 44.

Power source 48 may be any type of stored-energy source, includingelectrical or chemical-energy sources, suitable for powering theoperation of active stylus 20. In particular embodiments, power source48 may be charged by energy from a user or device. As an example and notby way of limitation, power source 48 may be a rechargeable battery thatmay be charged by motion induced on active stylus 20. In otherparticular embodiments, power source 48 of active stylus 20 may providepower to or receive power from the device or other external powersource. As an example and not by way of limitation, power may beinductively transferred between power source 48 and a power source ofthe device or another external power source, such as a wireless powertransmitter. Power source may also be powered by a wired connectionthrough an applicable port coupled to a suitable power source.

FIG. 4 illustrates an example active stylus 20 with an example device52. Device 52 may have a display (not shown) and a touch sensor with atouch-sensitive area 54. Device 52 display may be a liquid crystaldisplay (LCD), a LED display, a LED-backlight LCD, or other suitabledisplay and may be visible though a cover panel and substrate (and thedrive and sense electrodes of the touch sensor disposed on it) of device52. Although this disclosure describes a particular device display andparticular display types, this disclosure contemplates any suitabledevice display and any suitable display types.

Device 52 electronics may provide the functionality of device 52. Asexample and not by way of limitation, device 52 electronics may includecircuitry or other electronics for wireless communication to or fromdevice 52, execute programming on device 52, generating graphical orother user interfaces (UIs) for device 52 display to display to a user,managing power to device 52 from a battery or other power source, takingstill pictures, recording video, other suitable functionality, or anysuitable combination of these. Although this disclosure describesparticular device electronics providing particular functionality of aparticular device, this disclosure contemplates any suitable deviceelectronics providing any suitable functionality of any suitable device.

In particular embodiments, active stylus 20 and device 52 may besynchronized prior to communication of data between active stylus 20 anddevice 52. As an example and not by way of limitation, active stylus 20may be synchronized to device 52 through a pre-determined bit sequencetransmitted by the touch sensor of device 52. As another example, activestylus 20 may be synchronized to device by processing the drive signaltransmitted by drive electrodes of the touch sensor of device 52. Activestylus 20 may interact or communicate with device 52 when active stylus20 is brought in contact with or in proximity to touch-sensitive area 54of the touch sensor of device 52. In particular embodiments, interactionbetween active stylus 20 and device 52 may be capacitive or inductive.As an example and not by way of limitation, when active stylus 20 isbrought in contact with or in the proximity of touch-sensitive area 54of device 52, signals generated by active stylus 20 may influencecapacitive nodes of touch-sensitive area of device 52 or vice versa. Asanother example, a power source of active stylus 20 may be inductivelycharged through the touch sensor of device 52, or vice versa. Althoughthis disclosure describes particular interactions and communicationsbetween active stylus 20 and device 52, this disclosure contemplates anysuitable interactions and communications through any suitable means,such as mechanical forces, current, voltage, or electromagnetic fields.

In particular embodiments, measurement signal from the sensors of activestylus 20 may initiate, provide for, or terminate interactions betweenactive stylus 20 and one or more devices 52 or one or more users, asdescribed above. Interaction between active stylus 20 and device 52 mayoccur when active stylus 20 is contacting or in proximity to device 52.As an example and not by way of limitation, a user may perform a gestureor sequence of gestures, such as shaking or inverting active stylus 20,whilst active stylus 20 is hovering above touch-sensitive area 54 ofdevice 52. Active stylus may interact with device 52 based on thegesture performed with active stylus 20 to initiate a pre-determinedfunction, such as authenticating a user associated with active stylus 20or device 52. Although this disclosure describes particular movementsproviding particular types of interactions between active stylus 20 anddevice 52, this disclosure contemplates any suitable movementinfluencing any suitable interaction in any suitable way.

FIG. 5 illustrates an example force sensor of the example stylus of FIG.3. As described above, applying force to tip 26 of active stylus 20 mayinitiate a pre-determined function or gesture executed by active stylus20 or by the device. The amount of force applied to tip 26 is measuredby a force sensor 42 located within the interior of active stylus 20. Inparticular embodiments, pre-determined functions or gestures areinitiated at pre-determined force threshold levels. As an example andnot by way of limitation, initial contact by tip 26 on touch-sensitivearea of the device may initiate communication of data from active stylus20 to the device corresponding to device settings associated with aparticular user. Increasing the amount of force above a second thresholdlevel may initiate execution of a particular program by the device.

In particular embodiments, force sensor 42 may be implemented as acapacitive sensor or a mechanical sensor. As an example and not by wayof limitation, force sensor 42 may be formed from a printed circuitboard (PCB) 60 that mechanically support internal components (e.g.controller 50) of active stylus 20. In particular embodiments, PCB 60 isa multi-layer PCB with alternating layers of conductive (e.g. metal) andinsulating material. In other particular embodiments, force sensor 42formed using PCB 60 includes a spring structure 62 and electrodes 64 and66 separated by an air gap 68. As an example and not by way oflimitation, spring structure 62 is a flexible portion of force sensor 42that experiences a displacement proportional to an applied force. Springstructure 62 is coupled to center shaft 41, that in turn is coupled totip 26 of active stylus 20. In particular embodiments, spring structure62 of force sensor 42 is formed from substantially serpentine cuts inPCB 60. Moreover, the substantially serpentine cuts may be substantiallysymmetric with respect to a longitudinal axis defined by center shaft 41of active stylus 20. Although this disclosure describes and illustratesimplementation of force sensor 42 through cuts in PCB 60 having aparticular symmetry, this disclosure contemplates implementation offorce sensor 42 through any suitable arrangements of cuts in PCB 60. Inother particular embodiments, cutout portion 70 or void of springstructure 62 provides for displacement of portion of the springstructure 62.

Electrodes 64 and 66 may be formed from one or more metal layers of PCB60. In particular embodiments, exposed conductive material of exterioredges (i.e. proximate to outer body 22) of the substantially serpentinecuts forms moving electrodes 64 of force sensor 42. Exposed conductivematerial of inner edges of the substantially serpentine cuts formsstationary electrodes 66 of force sensor 42. In particular embodiments,the substantially serpentine cuts are substantially symmetric withrespect to a longitudinal axis of the active stylus. As an example andnot by way of limitation, one or more conductive layers of PCB 60 areused to form moving electrodes 64 and one or more different conductivelayers of PCB 60 are used to form stationary electrodes 66. Inparticular embodiments, moving electrodes 64 and stationary electrodes66 are coupled to controller 50 through appropriate routing and vias inPCB 60.

Controller 50 measures the capacitance between stationary electrodes 66and moving electrodes 64 at an initial position without force applied onspring structure 62. When tip 26 is depressed on a surface, force isexerted on spring structure 62 of force sensor 42 through center shaft41. The applied force on spring structure 62 causes a displacement of aportion of the spring structure in the area surrounding cutout portion70. Displacement of the portion of spring structure 62 causes movementof moving electrodes 64 relative to the position of stationaryelectrodes 66, resulting in a change of the distance of air gap 68between moving electrodes 64 and stationary electrodes 66. Movement ofmoving electrodes 64 relative to the position of stationary electrodes66 may be measured as a change of capacitance relative to the measuredcapacitance without force being applied to tip 26.

Force sensor 42 may be adjusted to compensate for the effect of tiltingactive stylus 20 on the force measurements. In particular embodiments,another force sensor 42 may be stacked above or underneath and inparallel to each other to determine the force applied to stylus 41through a common-mode signal between the two force sensors 42. As anexample and not by way of limitation, signals corresponding to a changeof capacitance relative to the measured capacitance without force beingapplied to tip 26 may be measured by both force sensors 42 and averagedto compensate for any tilt component. In other particular embodiments,the substantially serpentine cuts are substantially asymmetric withrespect to a longitudinal axis of the active stylus to determine theforce applied to stylus 41 through a ratio of signals having amulti-spatial wavelength. As an example and not by way of limitation, adensity of or spacing between serpentine cuts on one side of thelongitudinal axis may vary from the density of serpentine cuts on oneside of the longitudinal axis. Tilting of active stylus 20 will affecteach set of serpentine cuts differently depending on the location of thetilt relative to the longitudinal axis of active stylus 20. Signalscorresponding to a change of capacitance relative to the measuredcapacitance without force being applied to tip 26 may be measuredseparately measured for each set of serpentine cuts and averaged tocompensate for any tilt component.

FIG. 6 illustrates an example method for measuring force applied to anactive stylus. The method starts at step 100, where movement of a springstructure of a force sensor coupled to a center shaft of an activestylus is detected. In particular embodiments, movement of the springstructure may be detected through a change of capacitance from aninitial value without force being applied to the spring structure. Step102 measures a change of capacitance between the electrodes of the forcesensor. In particular embodiments, the moving and stationary electrodesof the force sensor are formed from metal layers of the PCB. At step104, an amount of force applied to the center shaft based on the changeof capacitance is determined, at which point the method may end. Inparticular embodiments, a pre-determined function is initiated when theamount of force applied to the center shaft is above a pre-determinedthreshold value. As an example and not by way of limitation, thecontroller of the active stylus may detect an amount of force applied tothe tip above a pre-determined threshold level and communicate a signalto initiate a pre-determined function or gesture to be executed by thedevice, as described above. As another example, the controller of theactive stylus may detect an amount of force above a pre-determinedthreshold and alter functionality of the active stylus. Although thisdisclosure describes and illustrates particular steps of the method ofFIG. 6 as occurring in a particular order, this disclosure contemplatesany suitable steps of the method of FIG. 6 occurring in any suitableorder. Moreover, although this disclosure describes and illustratesparticular components carrying out particular steps of the method ofFIG. 6, this disclosure contemplates any suitable combination of anysuitable components carrying out any suitable steps of the method ofFIG. 6.

Herein, reference to a computer-readable storage medium encompasses oneor more non-transitory, tangible computer-readable storage mediapossessing structure. As an example and not by way of limitation, acomputer-readable storage medium may include a semiconductor-based orother integrated circuit (IC) (such, as for example, afield-programmable gate array (FPGA) or an application-specific IC(ASIC)), a hard disk, an HDD, a hybrid hard drive (HHD), an opticaldisc, an optical disc drive (ODD), a magneto-optical disc, amagneto-optical drive, a floppy disk, a floppy disk drive (FDD),magnetic tape, a holographic storage medium, a solid-state drive (SSD),a RAM-drive, a SECURE DIGITAL card, a SECURE DIGITAL drive, or anothersuitable computer-readable storage medium or a combination of two ormore of these, where appropriate. Herein, reference to acomputer-readable storage medium excludes any medium that is noteligible for patent protection under 35 U.S.C. §101. Herein, referenceto a computer-readable storage medium excludes transitory forms ofsignal transmission (such as a propagating electrical or electromagneticsignal per se) to the extent that they are not eligible for patentprotection under 35 U.S.C. §101. A computer-readable non-transitorystorage medium may be volatile, non-volatile, or a combination ofvolatile and non-volatile, where appropriate.

Herein, “or” is inclusive and not exclusive, unless expressly indicatedotherwise or indicated otherwise by context. Therefore, herein, “A or B”means “A, B, or both,” unless expressly indicated otherwise or indicatedotherwise by context. Moreover, “and” is both joint and several, unlessexpressly indicated otherwise or indicated otherwise by context.Therefore, herein, “A and B” means “A and B, jointly or severally,”unless expressly indicated otherwise or indicated otherwise by context.

This disclosure encompasses all changes, substitutions, variations,alterations, and modifications to the example embodiments herein that aperson having ordinary skill in the art would comprehend. Similarly,where appropriate, the appended claims encompass all changes,substitutions, variations, alterations, and modifications to the exampleembodiments herein that a person having ordinary skill in the art wouldcomprehend. Moreover, reference in the appended claims to an apparatusor system or a component of an apparatus or system being adapted to,arranged to, capable of, configured to, enabled to, operable to, oroperative to perform a particular function encompasses that apparatus,system, component, whether or not it or that particular function isactivated, turned on, or unlocked, as long as that apparatus, system, orcomponent is so adapted, arranged, capable, configured, enabled,operable, or operative.

What is claimed is:
 1. A method comprising: detecting movement of aspring structure of a force sensor coupled to a center shaft of anactive stylus; measuring a change of capacitance between a pluralityelectrodes of the force sensor; and determining an amount of forceapplied to the center shaft based on the change of capacitance.
 2. Themethod of claim 1, wherein the spring structure being formed through aplurality of substantially serpentine cuts in a printed circuit board(PCB) of the active stylus, the electrodes comprising a moving electrodeand a stationary electrode being formed in the substantially serpentinecuts from a metal layer of the PCB.
 3. The method of claim 2, whereinthe substantially serpentine cuts are located at a end of the PCBproximate to the center shaft.
 4. The method of claim 2, wherein thesubstantially serpentine cuts are substantially symmetric with respectto a longitudinal axis of the active stylus.
 5. The method of claim 2,wherein the spring structure comprising a cutout portion in the PCBseparating one portion of substantially serpentine cuts from anotherportion of substantially serpentine cuts.
 6. The method of claim 2,wherein the force sensor comprising an air gap separating the movingelectrodes from the stationary electrodes.
 7. The method of claim 1,wherein a tilt component on the measured force is compensated byaveraging a common-mode signal or determining a ratio of signals havinga multi-spatial wavelength.
 8. One or more computer-readablenon-transitory storage media embodying logic configured when executedto: detect movement of a spring structure of a force sensor coupled to acenter shaft of an active stylus; measure a change of capacitancebetween a plurality electrodes of the force sensor; and determine anamount of force applied to the center shaft based on the change ofcapacitance.
 9. The media of claim 8, wherein the spring structure beingformed through a plurality of substantially serpentine cuts in a printedcircuit board (PCB) of the active stylus, e electrodes comprise a movingelectrode and a stationary electrode being formed in the substantiallyserpentine cuts from a metal layer of the PCB.
 10. The media of claim 9,wherein the substantially serpentine cuts are located at a end of thePCB proximate to the center shaft.
 11. The media of claim 9, wherein thesubstantially serpentine cuts are substantially symmetric with respectto a longitudinal axis of the active stylus.
 12. The media of claim 9,wherein the spring structure comprises a cutout portion in the PCBseparating one portion of substantially serpentine cuts from anotherportion of substantially serpentine cuts.
 13. The media of claim 8,wherein a tilt component on the measured force is compensated byaveraging a common-mode signal or determining a ratio of signals havinga multi-spatial wavelength.
 14. A device comprising: a force sensorcomprising: a spring structure of a force sensor coupled to a centershaft of an active stylus; and a plurality of electrodes; and acontroller configured to receive a signal from the force sensorindicative of a change of capacitance between the electrodes anddetermining an amount of force applied to the center shaft based on thechange of capacitance.
 15. The device of claim 14, wherein the springstructure being formed through a plurality of substantially serpentinecuts in a printed circuit board (PCB) of the active stylus, theelectrodes comprise a moving electrode and a stationary electrode beingformed in the cuts from a metal layer of the PCB.
 16. The device ofclaim 15, wherein the substantially serpentine cuts are located at a endof the PCB proximate to the center shaft.
 17. The device of claim 15,wherein the substantially serpentine cuts are substantially symmetricwith respect to a longitudinal axis of the active stylus.
 18. The deviceof claim 15, wherein the spring structure comprises a cutout portion inthe PCB separating one portion of substantially serpentine cuts fromanother portion of substantially serpentine cuts.
 19. The device ofclaim 15, wherein the force sensor comprises an air gap separating themoving electrodes from the stationary electrodes.
 20. The device ofclaim 14, wherein a tilt component on the measured force is compensatedby averaging a common-mode signal or determining a ratio of signalshaving a multi-spatial wavelength.